/Engine/Source/Developer/SkeletalMeshUtilitiesCommon/Public/LODUtilities.h
DestinationSkeletalMesh - Skeletal mesh receiving the LOD data.  SourceSkeletalMesh - Skeletal mesh providing the LOD data we want to use to add or modify the specified destination LOD at LodIndex. The LOD we want to import is always the base LOD of the source mesh.  LodIndex - The destination lod index we want to add or modify.  SourceDataFilename - The file name we use to import the source skeletal mesh.
static bool SetCustomLOD ( [USkeletalMesh](API\Runtime\Engine\Engine\USkeletalMesh) * DestinationSkeletalMesh, [USkeletalMesh](API\Runtime\Engine\Engine\USkeletalMesh) * SourceSkeletalMesh, const int32 LodIndex, const [FString](API\Runtime\Core\Containers\FString) & SourceDataFilename )